Add support for tick.mode and tick.source

- Replace getSampleSize() with getBarPixelsForIndex()
- Remove the ruler
- calculateBarIndexPixels() calls getBarPixelsForIndex() instead of using the ruler
- Add dataMin and dataMax to scale._model for scale adjustment in buildTick()
- Calculation of the bar size based on the tick interval for given time

src/scales/scale.time.js

@@ -517,21 +517,31 @@ module.exports = function(Chart) {
 			}
 
 			// If the chart has bars, shift min and max based on the sample size
-			if (me.options.gridLines.offsetGridLines || me.chart.hasBar) {
-				var sampleSizeMs = moment.duration(me.options.sampleSize || 0).asMilliseconds();
-				var offsetGridLines = me.options.gridLines.offsetGridLines;
-				var minOffset, maxOffset;
-				if (sampleSizeMs) {
-					minOffset = offsetGridLines ? 0 : - sampleSizeMs / 2;
-					maxOffset = offsetGridLines ? sampleSizeMs : sampleSizeMs / 2;
-				} else {
-					var tickSizeMs = (ticks.length < 2) ? max - min :
-						(ticks[ticks.length - 1] - ticks[0]) / (ticks.length - 1);
-					minOffset = offsetGridLines ? 0 : - tickSizeMs / 2;
-					maxOffset = offsetGridLines ? tickSizeMs : tickSizeMs / 2;
+			if (offsetGridLines || me.chart.hasBar) {
+				dataMin = model.dataMin;
+				dataMax = model.dataMax;
+				duration = max - min;
+				sampleSizeMs = moment.duration(me.options.sampleSize || 0).asMilliseconds();
+
+				tickSizeMs = duration;
+				for (i = 0, ilen = ticks.length - 1; i < ilen; ++i) {
+					tickSizeMs = ticks[i + 1] - ticks[i];
+					if (dataMin < ticks[i + 1]) {
+						break;
+					}
 				}
-				min = Math.min(min, model.min + minOffset);
-				max = Math.max(max, model.max + maxOffset);
+				size = sampleSizeMs || tickSizeMs;
+				min = Math.min(min, dataMin - (offsetGridLines ? 0 : size / 2));
+
+				tickSizeMs = duration;
+				for (i = ticks.length - 1; i > 0; --i) {
+					tickSizeMs = ticks[i] - ticks[i - 1];
+					if (dataMin >= ticks[i - 1]) {
+						break;
+					}
+				}
+				size = sampleSizeMs || tickSizeMs;
+				max = Math.max(max, dataMax + (offsetGridLines ? size : size / 2));
 
 				// Disable zero line if min has been updated
 				if (min !== helpers.min(ticks)) {
@@ -618,7 +628,6 @@ module.exports = function(Chart) {
 
 		getPixelForValue: function(value, index, datasetIndex, includeOffset) {
 			var me = this;
-			var ticks = me.ticks;
 			var time = null;
 
 			if (index !== undefined && datasetIndex !== undefined) {